There are a number of neurological events and conditions which are characterized by abnormal neural-electric activity in the brain including epilepsy, migraine headaches and even some forms of depression. Epilepsy is a disease characterized by recurrent unprovoked seizures which result in episodic impairment or loss of consciousness, abnormal motor phenomena, psychic or sensory disturbances, or the perturbation of the autonomic nervous system. It is caused by abnormal firing of neurons in the brain, a condition known as epileptogensis. These abnormal firings or electrical discharges may start in small neuronal populations (these are known as epileptogenci foci, the condition defined as focal epilepsy) or much larger areas of the brain (this condition is defined as generalized epilepsy). Often there can be a period of abnormal firing of neurons which precedes the full blown seizure. This period is known as a pre-seizure state and it can include one or more events of abnormal firing, known as pre-seizure events.
Whatever the cause, the human and financial impact of the disease is significant. The prevalence of epilepsy in the US is currently about three million, world-wide about fifty million, with 200,000 new cases diagnosed each year in the US alone. Ten percent of the American population will experience a seizure in their lifetime. Due to the impairing nature of epileptic seizures, the disease can prevent patients from performing a number of routine activities including driving car or operation of machinery. Many states put driving restrictions on those diagnosed with epilepsy. In a sub-population of patients, the severity of the disease is so extreme that they are essentially incapacitated. The economic cost of the disease is estimated to be $12.5 billion per year in direct and indirect costs.
While there are a number of available drug therapies for the treatment of epilepsy, these therapies have a number of side effects including hyperplasia, slurred speech and memory loss in large part due to the higher dose of drug which must be given systemically in order for the drug to reach the brain. They also require precise control of the therapeutic dosage to avoid occurrence of seizures for too low a dose or side effects for too high a dose. Thus, there is a need for improved methods for the treatment of neurological conditions such as epilepsy using drug therapy.
The current trend in many medical treatments requires the delivery of a drug to a specific target site so as to avoid the toxicity to other tissue and more precisely, as well controlling the timing and amount of drug delivered to that site. In many cases, this can require an implantable drug pump. However, due to their size and power requirements the current available pumps do not lend themselves to all medical applications, particularly for delivery of medication to the brain (e.g., for the treatment of various neurological conditions), where very precisely controlled doses of drug can be required. Also current devices can require frequent replenishment of the drug due to limited reservoir size and/or limited shelf life of the drug. Thus, there is a need for improved implantable drug delivery devices and associated methods for in vivo drug delivery of various neurological conditions.